effects of potassium metabisulfite pre-treatment and...

JOURNAL OF HORTICULTURE AND POSTHARVEST RESEARCH 2018, VOL. 1(1), 49-62

Journal homepage: www.jhpr.birjand.ac.ir

University of

Birjand

Effects of potassium metabisulfite pre-treatment and different

drying temperatures on some chemical properties and color

retention of Russian olive (Elaeagnus angustifolia) fruit

5and Sohrab Mahmoodi 4, Farid Moradinezhad3, Saeed Moodi2, Hashem Amini1*Mehdi Khayyat 1, 2, 4 Department of Horticultural Science, College of Agriculture, University of Birjand, Birjand, Iran

3, Department of Plant Pathology, College of Agriculture, University of Birjand, Birjand, Iran

5, Department of Agronomy and Plant Breeding, College of Agriculture, University of Birjand, Birjand, Iran

A R T I C L E I N F O

A B S T R A C T

Article history:

Received 5 December 2017

Revised 18 February 2018

Accepted 05 March 2018

Available online 09 March 2018

Keywords:

air-drying temperature browning index potassium meta-bisulfite weight loss

DOI: 10.22077/jhpr.2018.1177.1004

P-ISSN: 2588-4883

E-ISSN: 2588-6169

*Corresponding author:

Department of Horticultural Science,

College of Agriculture, University of

Birjand, Birjand, Iran, P.O. Box 331.

E-mail: [email protected] © This article is open access and licensed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/) which permits unrestricted, use, distribution and reproduction in any medium, or format for any purpose, even commercially provided the work is properly cited.

Silverberry is an important medicinal fruit that used for reducing pain. The present work was carried out to study the effect of potassium metabisulfite (KMS) and air drying temperature on quality of Russian olive fruit. Different KMS levels (0, 1, 2 and 4%) and drying temperatures (45, 60 and 75 °C) were used and some traits such as weight loss (WL), rehydration ratio (RH-R), TSS (total soluble solids), TA (total acidity), TSS/TA ratio, ascorbic acid, color parameters (L*, a*, b*, chroma and Hue, TEPL, TEPa and TEPb, ΔE and BI), total phenol (TP), and potassium were measured. WL, RH-R and total color change (ΔE) increased with increment of pre-treatment concentration. All traits except TSS, were significantly affected by drying temperature. The TA, ascorbic acid and TP raised by increasing air temperature from 45 to 60 °C. Temperatures higher than 60 °C led to increase ΔE. Increment of temperature from 45 to 75 °C led to an increasing trend of browning index, a*, b* and chroma, however, L* (lightness) and hue angle decreased. In general, using higher KMS concentrations as pre-treatment improved weight loss during drying, however, significant color change observed and color retention significantly reduced. Drying temperature higher than 60 °C also increased browning index of Russian olive fruit, however, total phenols increased in parallel. Thus, it is suggested that drying temperatures lower than 60 °C may be good treatment for drying silverberry fruits.

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khayyat et al.

50 JOURNAL OF HORTICULTURE AND POSTHARVEST RESEARCH VOL. 1(1) MARCH 2018

INTRODUCTION

Russian olive or silverberry (Elaeagnus angustifolia L.), belongs to Elaeagnaceae family and

is a Eurasian tree (Asadiar et al., 2012). Its flowers are fragrant, insect-pollinated, and silvery

on the underside, covered with minute scales and fruits are reddish-brown, elliptic, 9-12 mm

long and 6-10 mm wide with whitish pulp (Cansev et al., 2011; Ersoy et al., 2013). Leaves are

alternate, simple, grayish-green, and are covered with minute scales. Because of richness in

antioxidants, phenols (benzoic acid, cinnamic acid) and flavonoids (myricetin, epigallocatechin

gallate), its fruit is considered as a functional food recently (Patel, 2014). In Iranian traditional

remedies, dried fruit or pulp’s powder and seed of this fruit have been used as an analgesic

agent for reducing of pain in rheumatoid arthritis. In addition, pharmacological studies have

shown muscle relaxant activity, antibacterial, anti-inflammatory and antinociceptive effects

(Karimi et al., 2010).

One of the most commonly used preservation methods for fruits and vegetables is drying,

by which longer shelf life is accomplished by reducing water activity (Prabhanjan et al., 1995)

that can be achievable by different drying techniques including sun drying, hot-air drying,

spray-drying, microwave drying, osmotic dehydration and freeze-drying (Chong & Law, 2011).

Barbosa-Canovas and Vega-Mercado (1996) suggested that mechanical air dehydration leads

to some advantages over sun drying, including (a) reduction in contamination, (b) uniformity

in the product, (c) shortening drying time and, (e) lower labor cost.

Several studies have been conducted on the effect of air temperature on physical properties

and nutritional quality of air-dried fruits and vegetables (Ashebir et al., 2009; Esmaeili Adabi,

2013; Garau et al., 2007; Madrau et al., 2009; Vega-Gálvez et al., 2009; Vega-Gálvez et al.,

2012). In Chinese jujube fruits, the increment of drying temperature (from 50 to 70 °C)

increased browning (Fang et al., 2009). Drying temperature significantly increased colorimetric

parameters of pear fruit, including a* and b* due to the non-enzymatic browning reaction, which

turned the samples more reddish and yellow when the temperature is rose (Mrad et al., 2012).

Ben Haj Said et al. (2013) stated that color characteristics of Allium roseum significantly change

by drying temperatures. Vega-Galvez et al. (2012) and López et al. (2013) reported that color

difference significantly increased with temperature increment.

Chemical pretreatments are also used to reduce drying time. Vásquez-Parra et al. (2013)

indicated that chemical pre-treatment decreased moisture content of gooseberry fruits. Eleyinmi

et al. (2002) showed that potassium metabisulfite increased dehydration index of pepper under

drying condition. Prajapati et al. (2009) stated that blanching with potassium metabisulfite

(KMS) before drying checks the enzymatic spoilage and also improves the color and texture of

the shreds.

The silverberry fruit pulp is whitish in maturity stage that affects its commercial value.

However, drying may influence its color. Drying temperature and potassium metabisulfite

dipping as a chemical pre-treatment may affect the colorimetric properties of Russian olive

fruits powder, but to the authors’ knowledge, there is no report in this regard.

Therefore, the objectives of this study were to determine a) the effect of drying temperature

on color degradation; b) influence of potassium metabisulfite as a chemical agent to increase

dehydration rate of fruit and c) interactive effects of these treatments on some quality attributes

of Russian olive fruit.

MATERIALS AND METHODS

Drying of silverberry fruit

JOURNAL OF HORTICULTURE AND POSTHARVEST RESEARCH VOL. 1(1) MARCH 2018 51

Sample preparation, chemical pre-treatment, and drying process

Fruit harvested at the mature stage from a commercial orchard, in Kashmar, Khorasan-e-Razavi

province, Iran, in September 2014. Harvested fruit then transported to the Horticultural

Laboratory of the University of Birjand, to detect defected fruits for future study. The initial

moisture content of fruit was 27±0.6% wet basis (wb) determined using the oven at 105 °C until

constant weight (AOAC, 2000). Fruits dipped in potassium metabisulfite (KMS) solution (0 as

control, 1, 2 and 4%) for 1 min 25 °C, then surface dried with absorbent paper. Pretreated

samples dried in a convective oven dryer (Binder FED-720, Germany) using three inlet

temperatures including 45 °C (as control), 60 °C and 75 °C with an air velocity of 0.75 m s-1 to

a final moisture content of about 10% wb. Air velocity measured by an anemometer (Adolf

Thies GmbH & Co. KG. Hauptstraße 76-37083 Göttingen, Germany). The pulp was removed

from seed, then packed and sealed in polyethylene bags and kept under 5±1 °C until used for

future studies.

Weight loss

Weight loss percentage of dried fruits during drying was calculated as followed (1):

Weight loss (%) =Wi−Ws

Wi× 100 (1)

Where wi is the initial (i) weight of fruit samples, and ws is the weight of fruit samples at sth

weighing time during the drying process (Fang et al., 2009).

Rehydration ratio (RH-R)

To determine the rehydration ratio, three dehydrated Russian olives without fissures were

selected and soaked in distilled water at a 1:10 ratio of fruit to distilled water (w/w).

Rehydration was carried out at 25 °C for 14 h. Then, the fruits were taken out from the water

and put onto an absorbent paper as long as there is no water on the fruit surface, at which time,

the weight of fruits was determined.

Rehydration ratio was calculated as follows (2):

𝑅𝐻 − 𝑅 =𝑚𝑒−𝑚0

𝑚0× 100 (2)

Where m0 and me were the weight of fruits at initial time and after 14 h of rehydration,

respectively, and RH-R is the rehydration ratio as percentage (Fang et al., 2009).

Color measurement

The color of pulp powder was evaluated using a colorimeter (TES 135, Shenzhen Youfu Tools

Co., Ltd. - Taiwan). Hunter color values including L*, a*, b*, chroma, and Hue were calculated

(McGuire, 1992), and used for all color differences. The total effect of pretreatment (TEP) on

color values of dehydrated fruits were calculated using the following equations (3, 4 and 5):

TEPL = LT – LC (3)

TEPa =aT – aC (4)

TEPb =bT – bC (5)

Where TEPL, TEPa, and TEPb are total effects of any treatments on L (brightness or

lightness), a (redness), and b (yellowness), respectively. Subscript T stands for treatment

concentrations (potassium metabisulfite at 1, 2 or 4%) while subscript C stands for control (0%).

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khayyat et al.


There are also three other derived color calculations including total color change parameter

(ΔE) (Maskan, 2001), the ratio of yellowness over redness (Y=b/a) (Batu, 2004) and browning

index (BI). Browning index represents the purity of brown color and is considered as an

important parameter associated with browning (Palou et al., 1999). The equations of derived

color measurements were as follows (6, 7 and 8) to calculate total color change affected by

pretreatments:

ΔE= [(TEPL) 2 + (TEPa) 2 + (TEPb) 2]0.5 (6)

The ratio of yellowness over redness (Y) was evaluated as followed:

Y =b

𝑎 (7)

Browning index (BI) was calculated as followed:

BI =[100(x−0.31)]

0.17 (8)

Where 𝑥 =(a+1.75L)

(5.645𝐿+𝑎)−3.012𝑏

Total soluble solids (TSS), titratable acidity (TA) and ascorbic acid

The TSS were measured using a hand-held refractometer (0-32 % Brix, Guang Zhou, China).

Two grams of fruit powder were added to 10 ml distilled water. The samples were then placed

into a water bath at 77.5 °C for 30 min, and finally transferred for 1 h to room temperature in

order to cool down. The solution was then filtered (using Whatman Filter Paper, Grade 2) and

one drop of the filtrated solution was used for refractometer reading as Brix (Fang et al., 2009).

The TA was measured by acid-alkali neutralization titration method. For this, 5 g of pulp

powder was dispersed in 20 ml distilled water and then heated by immersing in a water bath at

77.5 °C for 30 min. The solution was diluted with distilled water to a final volume of 50 ml in

a volumetric flask and then filtered (using Whatman Filter Paper, Grade 2). Five drops of

phenolphthalein were added to 10 ml of filtrate and titration was performed by 0.1 M NaOH

until the solution turned to pink for at least 30 s. TA was calculated using the following equation

(9):

Titratable acidity (%) =𝑉𝑁𝐴𝑘

𝑀× 100 (9)

Where V is the volume of consumption of NaOH, N is the concentration of NaOH, A is

the dilution factor, k is the conversion factor (0.067 for malic acid) and M is the sample weight

in g (Bi et al., 2014). These data were used to show TSS/TA ratio.

Vitamin C content was determined by the 2, 6-dichloroindophenol titration method as

described by Fang et al. (2009) with some modifications. The dried powder of pulp (5 g powder)

was dispersed in 10 ml of 3% meta phosphoric acid solution and then homogenate. The sample

solution was transferred into a 50 ml volumetric flask, diluted with an extraction solvent to the

volume of 50 ml and filtered (using Whatman Filter Paper, Grade 2). Then, 10 ml of filtrate

was transferred into a 50-ml conical flask, and finally, titration was done with 2, 6-

dichloroindophenol until the solution turned to pink and kept for at least 30 s. A calibration

curve was also prepared using ascorbic acid (Merck KGaA, Darmstadt, Germany) and results

were expressed mg ascorbic acid in 100 g of powder.

Total phenols

One g of pulp powder was extracted by the addition of 10 ml of 70% (v/v) aqueous methanol

(Merck KGaA, Darmstadt, Germany), after being shaken for 2 h at room temperature, and

centrifuged at 4000 × g for 10 min. Consequently, the supernatant was separated from the solid

particles and was analyzed for total phenolic content (TPC). Total phenolic content (TPC) was



estimated by Folin-Ciocalteau’s (FC) assay with some modifications (Makkar et al., 1993); 450

µl of distilled water was added to 50 µl of prepared extract. Then 250 µl of FC reagent (FC,

Merck KGaA, Darmstadt, Germany) (1 N) was added, vortex-mixed and left to stand for 5 min.

Next, 1.25 ml of Na2CO3.10H2O (20%, Merck KGaA, Darmstadt, Germany) was added to the

mixture and incubated for 40 min under dark conditions at room temperature. Finally, the

absorbance was measured at 725 nm using a spectrophotometer (Biospec 1601, Shimadzu,

Tokyo, Japan). A calibration curve was also prepared using gallic acid (Merck KGaA,

Darmstadt, Germany) and results were expressed as mg gallic acid per 100 g dry matter.

Potassium analysis

Oven-dried materials of fruit pulp of each replication were used. Dried samples of each replicate

were ground separately and ashed in a porcelain crucible at 550 °C for 6 h. Each of the yielded

white ash was added to 2 M hot hydrochloric acid (HCl), filtered into a 50-ml volumetric flask,

and finally topped to 50 ml with distilled water. Potassium (K) was measured on these solutions.

K was analyzed using a flame photometer (Corning 405, Corning, Halstead, Essex, UK).

Statistical analysis

The experiment was arranged in a completely randomized design as 4×3 factorial. Data were

analyzed with ANOVA using GenStat program (version 12.1, Copyright 2009, VSN

International Ltd., UK). Means were separated with Tukey test at 95% level of confidence.

Each treatment consisted of four replications and each replicate consisted of 250 g of pulp

powder.

RESULTS AND DISCUSSION

Weight loss (WL)

The WL increased with the increment of KMS concentration (Fig. 1) and also drying

temperature (Fig. 2) increment. The simple effect of KMS showed the highest WL with 4%

concentration and 60 and 75°C drying temperatures led to the highest values of this parameter

(Table 1). The increment of weight loss under KMS concentration increment was in agreement

with the finding of Ahmadzadeh Ghavidel and Ghiafeh Davoodi (2009) on tomato. Pangavhane

et al. (1999) found that the chemical dipping before drying reduced the drying time of the final

product. It is suggested that modification of skin structure by the highest KMS (4%) may result

in lowest internal resistance to water diffusion and thus, highest weight loss.

More WL observed in higher drying temperature that may be related to changes occurred

in the crystalline to amorphous in the waxy cuticle of fruits under high temperature and then

resulted in increased skin water permeability (Price et al., 2000).

Interactive effects of pre-treatment and drying temperature indicated the highest WL in

fruit pre-treated with potassium metabisulfite (2%) and drying temperature of 60 °C, however,

there were no significant differences with other treatments, with the exception of 0 and 4%

under 45 °C (data not shown).

Rehydration ratio (RH-R)

Rehydration ratio is affected by both KMS concentration and drying temperature (P ˂ 0.05),

although the interaction between those factors unaffected this variable. Regarding to simple

effects, the highest RH-R value obtained with 4% KMS or at 60 °C drying temperatures,

although there is no significant difference between 40 and 75 °C (Table 1). Fang et al. (2009)

on jujube showed that increment of drying temperature led to higher RH-R. Rehydration is a

khayyat et al.


complex process aimed at the restoration of previously dried materials in contact with water.

Any reduction in RH-R value may be due to cellular damage which led to modification of

osmotic properties of the cells, as well as lower diffusion of water through the surface during

rehydration (Kaymak‐Ertekin, 2002). Fang et al. (2009) reported that the degree of rehydration

is dependent on the degree of cellular and structural disruption.

Color

All color characteristics (L*, a*, b*, C and H°) were influenced by drying temperature (Table 2)

and interaction of KMS concentration × drying temperature (Table 4), although KMS alone

unaffected those values. The L* (representing lightness) value statistically decreased with

increasing temperature from 45 to 75 °C (P ˂ 0.0001) that may be due to a larger extension of

Maillard reaction leading to a darker fruit pulp color (Vega-Gálvez et al., 2009). The interaction

between KMS and temperature indicated the highest values for this variable with 45 °C in all

concentrations of KMS and 60 °C in 0% of KMS (Table 4). The highest a* (representing redness

and greenness) value was observed at 75 °C that was significant compared with other

temperatures (P ˂ 0.0001), which corresponded to the pulp powder becoming more reddish.

About of b* (representing yellowness) value, it was found that drying at higher temperatures

(75 °C) tended to give higher yellowness compared with other temperatures. This increase of

yellowness may be justified by the generation of brown products due to non-enzymatic

reactions (Oliveira et al., 2015). Generally, the color change in food materials during thermal

processing is caused by the reactions taking place, such as pigment degradation (especially

carotenoids and chlorophyll), and browning reactions such as Maillard condensation of hexoses

and amino components and the oxidation of ascorbic acid (Barreiro et al., 1997; Lee & Coates,

1999; Lozano & Ibarz, 1997).

The saturation index or chroma (C) and the hue angle (H°), as shown in Table 2, provide

more information about the spatial distribution of colors than direct values of tri-stimulus

measurements (Sigge et al., 2001). The increase in a* value denotes a redder chroma which is

indicative of the enzymatic or/and non-enzymatic reactions (Mrad et al., 2012). Data from

interactive effects of KMS and temperature showed the lowest hue angle value with all KMS

concentrations at 75 °C drying temperature (Table 4). The browning reactions occurring during

drying and enzymatic reactions due to polyphenol oxidase and Maillard are the contributing

factors to the color change of products (Mrad et al., 2012). Similar results were obtained during

hot-air drying of apple at 70 °C (Kutyła-Olesiuk et al., 2013).

y = 0.538x + 43.126

R² = 0.89

42

44

46

0 1 2 3 4 5

Wei

gh

t lo

ss (

%)

Potassium metabisulfite (%)

y = 0.0763x + 39.49

R² = 0.99

42

42.5

43

43.5

44

44.5

45

45.5

40 50 60 70 80

Wei

gh

t lo

ss (

%)

Temperature (°C)

Fig. 1. Correlation between potassium metabisulfite

and weight loss of fruit

Fig. 2. Correlation between drying temperature and

weight loss of fruit



Table 1. Effects of KMS pre-treatment and drying temperatures on weight loss and rehydration ratio of silverberry pulp

KMS (%) Weight loss (%) RH-R (%)

0 43.40b† 40.31b

1 43.58b 36.82b

2 43.78b 40.03b

4 45.51a 47.45a

Drying temperature (°C)

45 42.85b 37.48b

60 44.22a 46.89a

75 45.14a 39.08b

†Values with the same letter in the same column were not significantly different (P > 0.05) by Tukey test.

Table 2. Effects of drying temperatures on color characteristics of silverberry pulp

Drying temperature (°C) l a b chroma Hue

45 96.06a† 7.79b 22.03c 28.65a 72.10a

60 94.55b 8.13b 24.95b 26.23b 71.95a

75 89.92c 9.91a 26.87a 23.12c 69.77b


Table 3. Effects of drying temperatures on TEPL, TEP a, b/a and browning index of silverberry pulp

Drying temperature (°C) TEPL TEPa b/a BI

45 -0.058b† 0.9921a 2.937ab 31.58c

60 -1.744c 0.2452ab 3.085a 36.53b

75 2.259a -0.4879b 2.718b 43.13a


The highest and lowest values of TEPL were observed in 75 °C and 60 °C, respectively

(Table 3). The interaction between drying temperature and chemical pre-treatment indicated

the highest TEPL in 75 °C and 2% of pre-treatment, although had no difference with other

levels (0, 1 and 4%) under 75 °C. Moreover, under 60 °C drying temperature, a reducing trend

was observed about this variable with an increment of KMS concentration. The lowest change

in brightness was observed at 60°C with different levels of KMS (Table 4), thus drying

temperature should not be increased higher than 60 °C (Table 4). TEPa showed changes with

drying temperature and reduced linearly (Fig. 3; R2=1) as temperature increased, although there

was no significant difference between 60 and 75 °C (Table 3). Yellowness index (b/a)

significantly decreased as temperature increased from 60 to 75 °C (Table 3). In ureaddition,

browning index also significantly increased with temperature increment (Table 5, Fig. 4) and a

linear correlation (R2=0.99) was observed that was in agreement with Fang et al. (2009) on

Chinese jujube. The interaction between drying temperature and chemical pre-treatment

showed the highest value of this trait at 75 °C and all levels of KMS (Table 4).

The BI is a common indicator in sugar-containing products submitted to processes where

enzymatic and nonenzymatic browning take place (Pathare et al. 2013). Total color change (ΔE)

significantly affected by pre-treatment (Fig. 5) and increased with KMS concentrations

compared with control (0%), although there was no significant difference among 1, 2 or 4%

concentrations, which was in contrast with Ergünş and Tarhan (2006) report. Jokić et al. (2009)

who found that chemical pre-treatments decrease total color change. ΔE may result from

Maillard reaction leading to a darker pulp color (Vega-Gálvez et al., 2009), non-enzymatic

reactions (Oliveira et al., 2015) or pigment degradation (Barreiro et al., 1997; Lee & Coates,

1999; Lozano & Ibarz, 1997).

khayyat et al.


Table 4. Interactive effects of KMS pre-treatment × drying temperature on l, hue, TEPL, and BI of silverberry pulp

Temperature (°C) KMS (%) l Hue TEPL BI

45

0 96.11abc† 72.78a 0.000abcd 30.78e

1 96.98a 72.88a 0.863abcd 32.19cde

2 95.92abc 70.57cde -0.198abcd 31.25e

4 95.22abcd 72.18ab -0.898bcd 32.08de

60

0 96.30ab 71.63abc 0.000abcd 34.06cde

1 94.32bcd 72.62ab -1.979cd 36.23cde

2 93.54de 72.17ab -2.755d 39.18abc

4 94.06cd 71.38bcd -2.240d 36.63bcde

75

0 87.66g 69.11f 0.000abcd 45.48a

1 90.43f 69.99ef 2.771ab 43.41ab

2 91.69ef 70.20def 4.028a 39.13abcd

4 89.90f 69.77ef 2.238abc 44.49a


Table 5. Effects of KMS pre-treatment and drying temperatures on TA, TSS/TA ration and ascorbic acid of silverberry pulp

KMS

(%)

TA

(%)

TSS/TA

Ascorbic acid

(mg 100-1 g D.W.)

0 1.15b† 12.42a 1.98c

1 1.18b 12.39a 2.13b

2 1.18b 12.45a 2.15b

4 1.30a 11.51b 2.27a

Drying temperature (°C)

45 1.03c 13.97a 1.90c

60 1.32a 10.99c 2.30a

75 1.26b 11.62b 2.19b


Table 6. Interactive effects of KMS pre-treatment × drying temperature on TA, TSS/TA and ascorbic acid of silverberry pulp

Temperature

(°C)

KMS

(%)

TA

(%)

TSS/TA

Ascorbic acid

(mg 100-1 g D.W.)

45 0† 1.14fg 12.38bc 1.68c

1 1.02hi 14.10a 1.73c

2 0.98i 14.79a 2.10b

4 0.99i 14.63a 2.10b

60 0 1.21def 11.86cd 2.10b

1 1.34bc 10.73ef 2.45a

2 1.27cde 11.31cde 2.13b

4 1.44ab 10.06f 2.53a

75 0 1.11gh 13.02b 2.15b

1 1.18efg 12.34bc 2.20b

2 1.31cd 11.26de 2.23b

4 1.46a 9.87f 2.18b


Table 7. Effects of drying temperatures on total phenols of silverberry pulp

Temperature (°C) 45† 60 75

Total phenol (mg g-1 D.W.) 260.81c 323.01b 350.21a

†Values with the same letter in a row were not significantly different (P > 0.05) by Tukey test.

TSS, TA and ascorbic acid

The TSS was not statistically different for KMS concentrations, air temperature and their

interaction (data not shown) that was in disagreement with Vega-Gálvez et al. (2009) report on

red pepper. The highest TA value observed in 4% KMS that was significant compared with

others. The TA significantly affected by drying temperature and highest amounts of TA

obtained with 60 °C (Table 5) that was in agreement with Vega-Gálvez et al. (2009) on red



pepper. Interaction of KMS and drying temperature showed the highest TA in 4% KMS under

60 and 75 °C.

Application of KMS at 4% concentration was led to the lowest TSS/TA ratio (Table 5).

The increment of drying temperature from 45 to 75 °C reduced TSS/TA ratio (Table 5). The

interaction between pre-KMS and drying temperature (Table 6) showed the highest amount of

this ratio with 45°C, and 1, 2 or 4% of chemical treatment. It is suggested that increasing trend

of this ratio may be resulted from decreasing of TA and/ or increment of TSS that may result

from higher water loss and more concentrated soluble solids.

Application of KMS led to the increment of ascorbic acid and the highest value observed

in 4% KMS (Table 5). The increment of drying temperature resulted in increasing trend of this

variable, compared with 45 °C (Table 5). Interaction of KMS and temperature showed the

lowest rate of ascorbic acid in 0 and 1% KMS and 45 °C (Table 6). The mechanism of vitamin

C degradation is specific for each food system and is dependent on many factors, including pH,

other components contained in the food, and reducing or oxidizing conditions (Serpen &

Gökmen, 2007). In addition, Mrad et al. (2012) showed that drying of pear pieces at a

temperature of 60 °C (in comparison to drying at 30, 40 and 50 °C) can be considered as an

optimum for pear in order to achieve acceptable ascorbic acid content and shortening drying

time. However, some authors reported conflicting results about tomato (Demiray et al., 2013)

and Acerola residues (Nóbrega et al., 2014). Madrau et al. (2009) showed that there were no

significant differences between all drying temperatures (55 and 75 °C) on the vitamin C content

of apricot.

Total phenols

This variable unaffected with KMS or interaction of KMS and temperature, however, air

temperature has an important effect on it. A significant increment is observed at 60 and 75 °C,

compared with 45 °C (Table 7) that might be due to the availability of precursors of phenolic

molecules used by non-enzymatic interconversion (Que et al., 2008). Similarly, an increasing

trend observed in apricot and plum after drying with hot air (Madrau et al., 2009; Piga et al.,

2003). They stated that polyphenol oxidase activity strongly higher at low temperatures

(approximately 55 °C) and reduced at 75 °C. It is highly likely the reason for higher phenolic

content observed at higher drying temperatures in our study.

y = 0.3853x + 13.957

R² = 0.99

25

35

45

40 60 80

BI

Temperature (°C)

y = -0.0493x + 3.2098

R² = 1

-1

0

1

2

40 50 60 70 80

TE

Pa

Temperature (°C)

Fig. 3. Correlation between drying temperature and

TEPa

Fig. 4. Correlation between drying temperature

and browning index

khayyat et al.


Potassium content

Potassium concentration of pulp powder increased as KMS concentration increased (data not

shown), which was in agreement with findings of Eleyinmi et al. (2002) on pepper. Changes

in salt content over time depend on the original concentration of the dipping solution.

CONCLUSION

Some qualitative parameters of Russian olive fruit were studied after treatment with different

levels of KMS (0, 1, 2 or 4%) and hot-air oven drying (45, 60 or 75 °C). Color and phenolic

contents may be very important for this fruit after drying process.

Results indicated that increment of KMS concentration induced weight loss under drying

condition, but did not positive effect on color retention and increased ΔE. So, KMS pretreatment

just was effective to reduce drying time and not positive for color retention and/ or

improvement.

Drying temperature also significantly influenced total phenols and ΔE, and temperature

higher than 60 °C led to the increment of these traits and also browning index, which is not a

good trait. So, it is suggested that drying temperature used for this fruit should not be higher

than 60 °C to achieve a better quality and more bright color.

CONFLICT OF INTEREST

All authors stated that there is no conflict in their research.

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سولفیت پتاسیم و دماهای مختلف خشک کردن بر برخی تاثیر پیش تیمار متابی

خصوصیات شیمیایی و حفظ رنگ میوه سنجد

سهراب محمودی و ، هاشم امینی، سعید مودی، فرید مرادی نژادمهدی خیاط

چکیده

در جهت بررسی تاثیر پیش تیمار های مهم مورد استفاده برای کاهش درد است. این تحقیقنجد یکی از میوهس

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درجه سلسیوس( استفاده و 00و 00، 44درصد( و دمای هوای خشک کردن ) 4و 2، 1به عنوان شاهد، 0پتاسیم )

گیری مجدد، میزان مواد جامد محلول، اسیدیته قابل تیتراسیون، نسبت بت آبصفاتی از قبیل درصد کاهش وزن، نس

مواد جامد محلول به اسیدیته قابل تیتراسیون، اسید آسکوربیک، خصوصیات مرتبط با رنگ )روشنایی، قرمزی، زردی،

ل وشدن(، میزان فن ایکروما، زاویه هیو، تغییرات هرکدام از پارامترهای ذکر شده، تغییرات کلی رنگ، شاخص قهوه

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نای تمامی صفات به استثبر آن داری نشان داد. عالوه گیری مجدد و تغییرات کلی رنگ میوه سنجد افزایش معنیآب

تاثیر دمای هوای خشک کردن قرار گرفتند. افزایش دمای هوای خشک داری تحتمواد جامد محلول میوه بطور معنی

ل کل شد. ودرجه سلسیوس منتج به افزایش اسیدیته قابل تیتراسیون، اسید آسکوربیک و فن 00به 44کردن از

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بطورکلی، افزایش غلظت پیش تیمار شیمیایی متابی سولفیت پتاسیم کاهش روشنایی و زاویه هیو دچار کاهش گردید.

نیز گردید و حفظ رنگ را کاهش داد. در دار این حال سبب تغییر رنگ معنی داری افزایش داد، باوزن را بطور معنی

ای شدن و دار شاخص قهوهدرجه سلسیوس بطور موازی سبب افزایش معنی 00دمای هوای خشک کردن بیش از

درجه سلسیوس به عنوان یک تیمار خوب 00ل کل گردید. بنابراین، استفاده از هوای گرم با دمای کمتر از ومیزان فن

گردد.یشنهاد میبرای خشک کردن میوه سنجد پ

دمای هوای خشک کردن، شاخص قهوه ای شدن، متابی سولفیت پتاسیم، کاهش وزنکلمات کلیدی:

effects of potassium metabisulfite pre-treatment and...

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